Fracturing in open hole is a complex subject and has been studied and written about by various authors. Whether using explosives or fluid jets one of the problems with the initiated fractures is in the way they propagate. If the propagation pattern is more tortuous as the fractures emanate from the borehole an undesirable condition called screenout can occur that can dramatically decrease the well productivity after it is put on production.
Hydraulically fracturing from any borehole in any well orientation is complex because of the earth's ambient stress field operating in the area. This is complicated further because of the extreme stress concentrations that can occur along the borehole at various positions around the well. For instance, there are positions around the borehole that may be easier to create a tensile crack than other positions where extreme compressive pressures are preventing tensile failure. One way that has been suggested to minimize this condition is to use jets that create a series of fan shaped slots in the formation with the thinking that a series of coplanar cavities in the formation will result in decreased tortuosity. This concept is discussed in SPE 28761 Surjatmaadja, Abass and Brumley Elimination of Near-wellbore Tortuosities by Means of Hydrojetting (1994). Other references discus creating slots in the formation such as U.S. Pat. Nos. 7,017,665; 5,335,724; 5,494,103; 5,484,016 and US Publication 2009/0107680.
Other approaches oriented the jet nozzles at oblique angles to the wellbore to try to affect the way the fractures propagated. Some examples of such approaches are U.S. Pat. Nos. 7,159,660; 5,111,881; 6,938,690; 5,533,571; 5,499,678 and US Publications 2008/0083531 and 2009/0283260.
Other approaches involved some form of annulus pumping in conjunction with jet fracturing. Some examples of this technique are U.S. Pat. Nos. 7,278,486; 7,681,635; 7,343,974; 7,337,844; 7,237,612; 7,225,869; 6,779,607; 6,725,933; 6,719,054 and 6,662,874.
Jets mounted to telescoping assemblies have been suggested with the idea being that if the jet is brought closer to the formation the fracturing performance will improve. This was discussed in U.S. application Ser. No. 12/618,032 filed Nov. 13, 2009 called Open Hole Stimulation with Jet Tool and is commonly assigned to Baker Hughes Inc. In another variation of telescoping members used for fracturing the idea was to extend the telescoping members to the borehole wall and to set spaced packers in the annulus so as to avoid the need to cement and to allow production from the telescoping members after using some of them to initially fracture the formation. This was discussed in U.S. application Ser. No. 12/463,944 filed May 11, 2009 and entitled Fracturing with Telescoping Members and Sealing the Annular Space and is also commonly assigned.
The present invention uses telescoping members and drives them out against the borehole wall with sufficient force to mechanically initiate the fracture. The telescoping members can be driven out by flowing through them or displacing them forcefully from within a bottom hole assembly using mechanical force such as a wedge device or a swage that also affords the option of expanding the diameter of the tubular housing in which the telescoping members are located. The telescoping members can have a constriction in them to function as the jet or simply a through passage that will act as a fluid jet when sufficient fluid volume with enough differential pressure is delivered through the jet nozzles. In another embodiment the positioning of the jets around a housing so that there is at least one nozzle within 22.5° in either of two opposed directions from the location of where the circumferential stresses are expected to the least compressive stress concentration which is the same as the most tensile stress concentration so that the fractures formed are less tortuous and subsequent production is enhanced. The jets can be disposed in a single or multiple rows depending on the telescoping member size and the borehole diameter. By getting at least one nozzle close to the more stressed location in the formation at the borehole the fracture initiated and propagated will be less tortuous. These and other benefits of the present invention will be more readily understood by those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is determined by the appended claims.